1. Field of the Invention
The present invention relates to chemical nanostructures having multiple elements, such as nanotubes and nanoparticles, more specifically to nanotubes and nanoparticles containing the elements of boron, carbon and nitrogen, and more specifically to synthesis of such materials using a plasma jet or plume.
2. Related Art
Presented below is background information on certain aspects of the present invention as they may relate to technical features referred to in the detailed description, but not necessarily described in detail. That is, individual parts or methods used in the present invention may be described in greater detail in the materials discussed below, which materials may provide further guidance to those skilled in the art for making or using certain aspects of the present invention as claimed. The discussion below should not be construed as an admission as to the relevance of the information to any claims herein or the prior art effect of the material described.
Boron-nitride-containing nanotubes (BNNTs) and related materials have many unusual and potentially useful properties, including exceptional thermal conductivity, uniform electronic bandgap, high mechanical strength, white color, and functionalization capability. Different synthesis methods have been used to produce limited amounts of BNNTs, including arc growth, modified chemical vapor deposition, and laser vaporization. Unfortunately, all of these methods are not easily scaled up to meaningful industrial production levels. The synthesis bottleneck is the major reason BNNTs and related materials have not enjoyed widespread application.
Pure boron nitride nanotubes consist of alternating B—N bonds, arranged in a hexagonal pattern similar to that of carbon nanotubes. A boron nitride nanotube may be visualized essentially as a rolled on itself graphite-like sheet, where carbon atoms are alternately substituted by nitrogen and boron atoms. Structurally, it is a close analog of the carbon nanotube, namely a long cylinder with diameter on the order of one to about one hundred nanometers and length up to many microns or even centimeters. The properties of BNNTs nanotubes are very different from those of pure carbon nanotubes: whereas carbon nanotubes can be metallic or semiconducting depending on the rolling direction and radius, a BN nanotube may act as a semiconductor or an electrical insulator with a bandgap of ˜5.5 eV, basically independent of tube chirality and morphology. BNNTs have high resistance to oxidation and are structurally stable and inert to most chemicals. It would be useful to find a way to exploit the intrinsic properties of BNNTs for various materials and device applications. In order to do this, surface modification of the BNNT, including functionalization with small molecules, polymers, nanoparticles, and thin films, would be useful. In addition, a layered BN structure is much more thermally and chemically stable than a graphitic carbon structure.
Boron nitride nanotubes were theoretically predicted in 1994 (Cohen and coworkers) and first experimentally synthesized in 1995 (Zettl and coworkers, Science, 18 Aug. 1995: Vol. 269. no. 5226, pp. 966-967). Alloy and doped BNNTs have also been produced. Boron nitride thin sheets, analogous to graphene, have also been produced, and may be produced by the methods and apparatus described here.
Specific Patents and Publications
U.S. Pat. No. 6,063,243 to Zettl et al., issued May 16, 200, entitled “Method for making nanotubes and nanoparticles,” describes novel electrodes for use in arc discharge techniques. The electrodes have interior conduits for delivery and withdrawal of material from the arc region where product is formed. In one embodiment, the anode is optionally made from more than one material and is termed a compound anode. The materials used in the compound anode assist in the reaction that forms product in the arc region of the apparatus. The materials assist either by providing reaction ingredients, catalyst, or affecting the reaction kinetics. The device comprises an arc-discharge chamber provides a controllable ambient gas environment. In this apparatus, either the compound anode or the material injected through either of the electrodes and may be the source of material for product formation in the arc region. For example, to produce a product comprising nanotube and nanoparticles of sp2-bonded BxCyNz, an electrode may inject into the arc region, a type of gas comprising elements from the group consisting of boron, nitrogen and carbon. In that case, the anode may or may not include the element injected through the conduits of the cathode and the anode. The nanoparticles and nanotubes formed within the product deposited on the cathode comprise individual particles and tubes having inner diameters on the order of nanometers.
US US20090117021 by Smith et al., published May 7, 2009 entitled “Boron Nitride Nanotubes,” discloses a method in which boron nitride nanotubes are prepared by a process which includes: (a) creating a source of boron vapor; (b) mixing the boron vapor with nitrogen gas so that a mixture of boron vapor and nitrogen gas is present at a nucleation site, which is a surface, the nitrogen gas being provided at a pressure elevated above atmospheric, e.g., from greater than about 2 atmospheres up to about 250 atmospheres; and (c) harvesting boron nitride nanotubes, which are formed at the nucleation site. It also disclosed there that, since the announcement of the successful synthesis of high-aspect-ratio few-walled boron nitride nanotubes (FW-BNNTs) in 1995, little progress has been made in the scale-up of their synthesis.
US 2010/0051879 by Sainsbury et al., published Mar. 4, 2010, entitled “Functionalized Boron Nitride Nanotubes,” discloses that BNNTs can be synthesized on Si substrates by thermal decomposition of B and MgO powders in an ammonia environment at 1200° C. in an electric furnace.
U.S. Pat. No. 6,231,980 issued May 15, 2001, by Cohen et al., entitled “BxCyNz nanotubes and nanoparticles,” discloses crystalline nanoscale particles and tubes made from a variety of stoichiometries of BxCyNz where x, y, and z indicate a relative amount of each element compared to the others and where no more than one of x, y, or z are zero for a single stoichiometry. Anode rods of different structure and B—C—N composition were prepared and subsequently arced against pure graphite cathodes. A number of anode-type, arc current, and helium pressure combinations were investigated. BC2N nanotubes and BC3 nanotubes were produced using a high purity graphite rod (about 0.250-in. diameter) that was center drilled to slip-fit a high-purity, hot-pressed BN rod (about 0.125-in. diameter) inside.